TortoiseSVN is an easy-to-use SCM/source control software for Windows and possibly the best standalone Apache™ Subversion® client there is.

Since it's not an integration for a specific IDE, you can use it with whatever development tools you like. It is developed under the GPL, so it is completely free.

Key features:

• Most current CVS features.
• Directories, renames, and file meta-data are versioned.
• Commits are truly atomic.
• Branching and tagging are cheap (constant time) operations.
• Efficient handling of binary files.